2025/05/03 by Lei, Ming-Yu, Shen, Zhao-Qiang, Xia, Zi-Qing +1
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2505.01708
Millisecond pulsars (MSPs) are prominent GeV γ-ray emitters, but their emission mechanisms, especially during off-pulse phases and at high energies, remain debated. We analyze 38 MSPs using approximately 15 years of Fermi-LAT data. Employing high-precision ephemerides and Bayesian Blocks algorithm, we detect significant off-pulse emission from 15 MSPs. Spectral analysis reveals significant cutoffs in 10 of these, favoring a magnetospheric origin. The remaining 5 likely also have magnetospheric emission with cutoffs below current sensitivity. Phase-resolved spectral analysis for the 15 MSPs with off-pulse flux shows a significant correlation between cutoff energy (Ecut) and average photon counts in 11 sources. We introduce a phase-resolved pseudo-luminosity (L) and discover a novel, statistically significant linear correlation between log10(L) and log10(Ecut) across their phase bins, with the best-fit slope α= 2.31+0.22-0.25. Furthermore, we detect significant pulsed emission above 10 GeV from 9 MSPs with off-pulse emission and 7 others (totaling 16 MSPs and tripling previous cataloged detections). Emission above 25 GeV is confirmed for PSR J0614-3329 and newly detected for PSR J1536-4948, both of which also exhibit significant off-pulse emission. Their highest-energy photons (∼61 GeV and ∼57 GeV, respectively) coincide with pulse peaks. The co-existence of significant off-pulse emission and high-energy pulsed emission challenges standard Outer Gap models, while the observed log10(L)-log10(Ecut) correlation may provide new evidence supporting the equatorial current sheet scenario.